Throughout this application, various references are referred to. Disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains.
While more and more biological therapeutic agents have become available due to the advances in molecular biology, immunology and microbiology, pharmaceutical development (e.g. development of appropriate dosage forms) for delivery of these proteins is behind the state of art of biotechnology. The situation is attributed to the difficulties in formulating these agents which are less permeable to tissue membranes, highly degradable at the sites of administration and therapy, short shelf life, and structurally susceptible during conventional formulation processes. To develop commercially available and patient compliant dosage forms for these therapeutics, the above-mentioned issues must be addressed respectively.
The disclosed are a novel material system named polymer aqueous/aqueous emulsions and its pharmaceutical and biotechnological applications. To meet desired therapeutic purposes such as sustained release, targeting to therapeutic sites, extension of bio-activity, and reducing toxicity, many chemical and biological therapeutics need to be microencapsulated[1,2]. Emulsification is a key step in microencapsulation during which active ingredients are incorporated into the dispersed phase. Conventional emulsions are made by dispersing a hydrophilic phase (dispersed phase) into a hydrophobic phase (continuous phase) or vice versa (W/O or O/W)[3]. For microencapsulation of protein therapeutics, a double emulsification process, called water-in-oil-in-water (W/O/W) emulsification, is used. The protein solution is first dispersed into a polymer solution dissolved in an organic solvent, and the resulted emulsion is further dispersed into a dilute aqueous solution of another polymer, followed by solvent evaporation or extraction. The major problem associated with the conventional microencapsulation procedures is that the protein molecules may be denaturated by contacting with the organic solvents which are indispensable in the processes. Although surfactants and/or hydrogel solutions are used in the first emulsification to protect the proteins[4,5], they are only effective to certain relatively stable proteins. A microencapsulation process which is free of organic solvents is highly demanded.
For aqueous systems, particles may be formed through various precipitation mechanisms such as salting out[6], acid-base interaction[7], pH assistant precipitation. For these mechanisms, concentrated salts, extreme pH or protein (ionic) cross-link agents are unavoidable. These are all considered chemical hazards to the activity of biological therapeutics.
Two polymer aqueous solutions may be immicsible due to their chain length and structural difference[8]. Such polymer aqueous two-phase systems (which are not emulsions but block phases) are practically used for protein purification[8,9]. Their aqueous nature and relatively low interfacial tension provide excellent compatibility with soluble proteins in terms of preventing protein conformation change. Protein purification is based on their partition which favors one of the aqueous polymer phase with impurities partitioning into the other. The practice of protein purification is evident that proteins can be distributed into one of the aqueous phases with biological activity intact. This two-phase system readily forms two block phases after mixing. For microencapsulation purpose, however, a stable emulsion must be formed with the two polymer aqueous solutions.
This invention is aimed to address the above-mentioned issues and to develop a new formulation strategy for susceptible therapeutics especially biological agents.
The present invention provides a stable aqueous/aqueous emulsion system which is prepared with a hydrophilic polymer.
This invention also provides the method of preparing a stable aqueous/aqueous emulsion comprising steps of: a) selecting appropriate polymeric materials for dispersed phase and continuous phase which are immiscible, biocompatible and have biased partition to the active ingredients to be encapsulated; b) selecting appropriate surface modifiers which are charged, non-toxic, and possessing a moderate interfacial tension between the above two phases; c) developing phase diagram for the above; and d) dispersing the dispersed phase into the continuous phase under an appropriate shear stress.
Finally, the invention provides an encapsulation comprising the emulsion system which is prepared with a hydrophilic polymer.
The present invention demonstrates a stable emulsion system which provides the solution for all the problems raised above by that both the dispersed and the continuous phases are formed from aqueous solutions without concentrated salts, extreme pH, and other chemical hazards.
Water soluble proteins, liposomes, live viruses and other therapeutic agents can be microencapsulated on the bases of their partition favoring the dispersed phase, and released or reconstituted upon or prior to administration with their original morphology and activity preserved.
The emulsion can be dried to fine powder through freeze-drying, spray drying and other methods, and subjected to further treatment: coating, double-microencapsulation, compressing and other procedures by which a variety of pharmaceutical dosage forms including controlled release systems and targeted delivery systems can be prepared.
For biological agents including live viruses, encapsulation into the dry form can not only improve their stability and shelf-life, but also avoid expensive cold-chain (xe2x88x9220xc2x0 C.) in transportation and application. This is important for many developing countries where cold-chain is not available.
All the polymer materials used in the invented emulsion system (including dispersed phase, the continuous phase and the surface stabilizing agent) are biocompatible and good for internal use on humans.